1. Technical Field
The present invention relates generally to a device for suppressing high-voltage electricity, and more particularly to a method and device applied in vehicles to suppress high-voltage electricity generated in a generator.
2. Description of Related Art
In recent years, vehicles are driven by high power, so that the generator thereof should generate high-current electricity. The conventional rectification having a diode with a P-N junction can't afford such high-current electricity.
In present days, metal-oxide-semiconductor field-effect transistors (MOSFETs) are widely used since they could be switched fast, and have a lower forward bias to reduce the heat generating. For example, if a100A current is transmitted to a MOSFET with 1 mΩ conducting resistance (Rds(on)), there only is a potential drop of 0.1V. However, it will be 1.0V for a conventional diode, so that the MOSFET only generates one to tenth of the heat of the diode. The MOSFET in an electric generator may reduce the heat, and therefore it can save the heat dissipating device in the electric generator to reduce the weight, and save the energy.
However, for the electric generator installed in a vehicle, such as a micro hybrid vehicle with a start-stop system, it has to face the problem of load dump, which generates surge voltage. It is an important issue to deal with the surge voltage, which may damage electronic elements.
A conventional way of suppressing the surge voltage is cutting the generator off immediately while the surge voltage is appearing, and simultaneously conducting three MOSFETs of low arms to convert the energy of the surge voltage into heat. Typically, the surge voltage has high voltage and high energy, so that there will be an extreme high current transmitting through the MOSFETs, even there are many
MOSFETs. However, the current and the heat concentrate in three MOSFETs. Therefore, in practice, a chip with larger power and size and a heat sink with high thermal capacity are needed to solve this problem. However, it doesn't get a good result, and furthermore, such MOSFETs are very expensive.